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More than 40 million patients wear contact lenses in the United States, which equates to a $3 billion industry. Still, contact lens wearers have been and continue to be plagued by symptoms of ocular irritation.1 These symptoms are found in both rigid and soft contact lens wearers alike. Because almost 90% of the contact lens market is soft contact lenses, much of our focus rests on the problems associated with soft contact lens discomfort.

McMonnies and Ho were pioneers in recognizing and analyzing discomfort in contact lens wear.2 Over time, we have seen a plethora of papers supporting their initial observations. We have also observed a dramatic shift in the industry’s focus from its initial concerns with keratitis and safety3–5 to those of contact lens discomfort. As stated before, numerous studies have confirmed the early observation that up to 50% of contact lens wearers experience dryness or discomfort at least occasionally.6–8 The issue has become so complex that the Tear Film and Ocular Surface Society committed an entire workshop to studying this dilemma.1,9–11 Over 80 global experts in the field came together to study the problem of contact lens discomfort and make evidence-based, consensus summaries and recommendations about this problem. Two years later, we are now at the precipice of moving the field even further and are excited to bring some of the latest developments in this special issue of Optometry and Vision Science devoted to contact lens discomfort. Here are some of the exciting topics covered in this issue.

Subjective Outcomes

One major problem facing the contact lens industry and regulatory bodies is the low number of patient-based, subjective outcomes that can be used in clinical trials. The Contact Lens Dry Eye Questionnaire is validated and accessible, and its wide use has undeniably helped advance discoveries in the field.12–15 Nevertheless, it is completely symptom-based and does not reflect other important issues that may cause discomfort in contact lens wearers. As Basuthkar and Rao demonstrate in this issue,16 ratings of comfort are highly influenced by blur. Dumbleton and colleagues demonstrate that contact lens wearers have greater discomfort by the end of the day.17 Rueff and colleagues also report that presbyopic patients discontinue lens wear because of discomfort and poor vision.18 Keratoconus patients present unique problems of comfort and vision and Bergmanson and colleagues demonstrate that scleral lenses are a good answer.19 Keir and colleagues evaluate the impact of masking on subjective ratings assessments of contact lenses and showed that while masking did not have a measurable impact of various 0 to 100 ratings, it did have an impact on subjective lens preference.20 Patients were more likely to express a preference for a lens type when they were able to handle it and its package. Stahl and colleagues address an important study design issue—the impact of a washout period between lens assessments.21 These researchers found no effect of washout period when patients were reporting on end-of-day discomfort. This has important implications when studying contact lens comparisons both in studies and in clinic. Lastly, Wirth and colleagues present a new patient-based survey instrument developed using the latest methods, e.g. item banking, factor analysis, item response theory, computerized adaptive testing, etc.22 The authors have developed and validated this new tool specifically for contact lens wearers—the Contact Lens User Experience (CLUE) Scale. The CLUE questionnaire analyzes four different domains (comfort, vision, handling, and packaging) to understand a contact lens wearer’s subjective experience with contact lenses. It is hoped that the CLUE questionnaire will help with the development of new contact lenses. It is also hoped that the CLUE questionnaire can help advise eye care providers on how best to address their contact lens patients’ barriers to success.

Objective Outcomes

Although there is a clear need for more work to understand the patient’s contact lens experience, there is also a need for validated objective methods to assess contact lens discomfort. In particular, finding objective measures of patient comfort that correlate well with what contact lens wearers subjectively report is an open challenge. Although we believe that the pre-lens tear film is very dynamic and important to comfort and vision during contact lens wear, we do not understand much beyond that. Szczensa-Iskander and colleagues address this issue by assessing pre-lens tear film characteristics relative to the quality of the visual response.23 They develop and report on a new non-objective optical system that proved sensitive enough to detect a two-phase process of pre-lens tear film dynamics. It was shown that dewetting was related to the subjective response and a just-noticeable change in visual quality. Similar to this, Guillon and colleagues also report on the association between pre-lens tear film kinetics and subjective contact lens discomfort.24 In their work using the Tearscope, they showed that pre-lens tear film kinetics were worse in contact lens wearers with discomfort compared to those without discomfort. Gonzalez-Garcia and colleagues found no associations in any of the corneal sensory receptors or tear inflammatory mediators when comparing symptomatic and asymptomatic contact lens wearers.25 However, Situ and colleagues, using a Belmonte esthesiometer that was similar to that used by Gonzalez-Garcia, found that asymptomatic CL wearers had a higher cold detection sensitivity and greater intensity and irritation at stimulus detection than the asymptomatic wearers.26 Differences in methodology may partly explain these disparate findings. It was hypothesized in the TFOS Contact Lens Discomfort report on the ocular adnexa that subclinical lid papillae might be a cause of discomfort.27,28 Lievens and colleagues partly examined this by showing that the use of hydrogen peroxide disinfection can improve papillary changes observed in symptomatic wearers with discomfort.29 Although the role of contact lens edge shape was considered equivocal in the TFOS report on Contact Lens Discomfort,30 Tankam and colleagues provide a method for assessing edge shape, which may have a role in future research on edge shape and comfort.31 Dantam and colleagues assessed the contamination rates of contact lens cases, and although they did not assess correlations to comfort, this might be a fruitful area of future research. Masoudi and colleagues report that the concentration of prolactin-induced protein in tears is associated with contact lens discomfort, and this may lead to further research on the role of prolactin in tears and ocular sensation.32

Clinical Insights

The biocompatibility of contact lenses and their care solutions is a concern to researchers and clinicians. Several manuscripts report on a multisite, controlled clinical trial involving research teams at the University of Alabama at Birmingham, University of Houston, University of Manchester, and University of Waterloo. The goals of this large clinical trial were to examine the subjective and objective responses of contact lens wearers when wearing various silicone and hydrogel contact lenses in combination with several multipurpose contact lens care solutions and hydrogen peroxide. Berntsen and colleagues showed similar levels of comfort when using all combinations of contact lens materials and care solutions, with slight but not clinically meaningful increases in corneal staining (0.5 units) with several multipurpose solutions compared with hydrogen peroxide.33 In a related manuscript from the same study, Cox and colleagues report on lid margin characteristics in this large cohort of contact lens wearers.34 It is reported here that both mucocutaneous junction and meibomian gland expressibility have a significant impact on contact lens comfort, whereas other characteristics of the lid margin did not have an impact on comfort. From the same study cohort, Schulz and colleagues also evaluated and report on lid-wiper epitheliopathy.35 Lid-wiper epitheliopathy was shown to be present in a staggering 85% of this contact lens wearing cohort, yet was not related to contact lens comfort. This finding was, however, related to habitual lens type. In a completely independent study, Alzahrani and colleagues report on the inflammatory cell upregulation that occurs in the lid wiper area in contact lens wearers with discomfort.36 Using confocal microscopy, without histopathological confirmation, they report that Langerhans cells are upregulated in the lid wiper area of contact lens wearers with discomfort. Shigeyasu and colleagues report on the use of diquafosol, a P2Y2 purinogenic receptor agonist, for the treatment of dry eye.37 They report reductions in symptoms, improvement in tear breakup time, and ocular surface staining as the results of using diquafosol. Nichols and colleagues report that a carboxymethylcellulose and hyaluronic acid containing drop showed improvements in ocular symptoms after 90 days of use compared to control with a subsequent reduction in lid-wiper epitheliopathy.38 Lazon de la Jara and colleagues found that the demographics of contact lens wearers such as age, refractive error, and ethnicity affect contact lens discomfort ratings, indicating the importance of these variables in future clinical trials.39

Parting Thoughts

The purpose of this special issue of OVS is to bring you the most current research and thought about contact lens discomfort, which is likely the single biggest problem facing all stakeholders involved in the use of contact lenses: patients, practitioners, and the contact lens industry. Here, you will find a valuable collection of clinical insights, perspectives, basic discoveries on etiological factors, and methodological assessments all focused on the topic of contact lens comfort. This body of work is a source of optimism that we can reduce or even eliminate the problem of contact lens discomfort. We know that the information in this special issue will move us toward this goal and be of great value to you and your patients.